This invention relates to a breather apparatus for a 4-cycle engine.
In an engine, gas pressurized in the cylinder gradually leaks or blows-by into the crankcase through a separation between the piston and the cylinder bore. The pressure of the gas in the crankcase fluctuates as the piston slides, and if the crankcase is tightly sealed, piston movement is inhibited. Therefore, it is necessary to release the blow-by gas and to separate the sprayed oil mixed in the blow-by gas with a breather apparatus.
Japanese Unexamined Patent No. Hei-7-324614 is a typical breather apparatus in which one end of a breather passage connects to a breather chamber, thereby reducing the pressure of the blow-by gas and separating the oil in the blow-by gas. This apparatus"" efficiency depends on the size of the breather chamber, but as the size of the breather chamber is increased, so is the weight of the engine. Furthermore, the apparatus requires a maze structure and an orifice in the breather chamber in order to separate oil. This is a complicated structure. Finally, since the pressure where the separated lubrication oil is returned is greater than the atmospheric pressure, lubrication oil collection is difficult.
Japanese Unexamined Patent No. Hei-11-22443 discloses an apparatus in which blow-by gas is guided into a hollow balancer shaft where a disk-shaped member such as a balancer weight is located. This disk-shaped member includes an oil separating passage where the oil in the blow-by gas is separated. Although the breather chamber is eliminated, the balancer shaft diameter and layout must be exact, making the structure of the balancer shaft complicated.
The present invention addresses these problems and provides a simple breather apparatus for a 4-cycle engine which allows separation of oil in blow-by gas.
According to the present invention, in a 4-cycle engine, the inside of the crankcase is divided by a bulk head into two chambers: (1) the crank chamber that houses a crankshaft and (2) the transmission chamber in which a clutch body is supported by a counter shaft. An oil pan stores lubrication oil in each chamber. A pair of oil pumps are provided in the crank chamber, one of which takes in lubrication oil from the oil pan in the crank chamber and the other of which takes in lubrication oil from the oil pan in the transmission chamber. A kick engine starter is provided which transmits a rider""s pedal force to the crankshaft via a plurality of gears and includes a kick idle gear that transmits a rider""s pedal force to the crankshaft via a clutch body. A hollow kick idle shaft rotates with and supports one end of this kick idle gear and is located on the upper rear of the counter shaft in the transmission chamber so that at least a part of it overlays the clutch body when viewed from the side. A breather passage is provided in the kick idle shaft. A blow-by gas intake port is provided on the side end of the kick idle gear of the breather passage, and a blow-by gas exhaust port is provided on the end of its opposite side.
The kick idle gear may be arranged opposite to and facing the clutch body with the blow-by gas intake port, which communicates with the breather passage, in the kick idle shaft located on this kick idle gear.
A generator chamber, separate from the crankcase, may be located on the left side of the crankcase and lies on the crank and transmission chambers. A covered generator is housed in the generator chamber. Two holes connect the crank and transmission chambers to the lower and upper sides of the generator, respectively. A check valve in the upper hole restricts backflow from the transmission chamber to the generator chamber. The lower hole is placed above the lubrication oil level in the crank chamber""s oil pan.
In the breather apparatus for a 4-cycle engine of this present invention, oil in blow-by gas can be separated by a simple structure as described above, thus making a breather chamber unnecessary, and thereby allowing the engine structure to be more compact, lightweight and simple. Furthermore, when guiding blow-by gas from the crank chamber to the transmission chamber, the lubrication oil does not flow into the transmission chamber, and the blow-by gas does not back-flow into the crank chamber. In addition, the lubrication oil in the crank chamber""s oil pan does not flow into the generator chamber.